In this work, we propose a simple way to effectively implement active control of laser injection locking without requiring additional bulky devices. We employ a photodetector and a narrow laser-line filter to probe the spectral mode of slave laser, which can be easily integrated into the beam path. The spectral mode of slave laser is monitored through the reflected signal from the narrow-laser line filter, which is neither sensitive to beam alignment nor bandwidth limited. With a simple feedback to the slave laser current, we demonstrate that high spectral mode purity and low intensity noise of the slave laser can be simultaneously obtained. We also show that the slave laser can be locked even when the master laser frequency is dynamically scanned over GHz range. We have successfully applied this method in laser cooling and trapping of erbium atoms towards degenerate dipolar quantum gases [1]}, [2]}. Our method paves the way towards general applications of injection locking. A promising scenario is coherent addition of multiple laser diodes for light power scaling, where injection locking plays a fundamental role [3]}.
